The objective of this proposal is to derive a pluripotential embryonic stem (ES) cell line from the rabbit for the purpose of creating rabbit models of human disease. Cell lines will be derived from the inner cell mass cells of explanted rabbit embryos in the presence of appropriate feeder layers and other conditions necessary for growth and maintenance of the undifferentiated (pluripotential) state of the cells through serial passage. Male (XY) ES lines will be identified using a Y chromosome-specific probe, and characterized in terms of: (1) Ability to form embryoid bodies and to differentiated into cell types characteristic of the three germ layers, (2) Ability to colonize the normal rabbit embryo following introduction into recipient blastocysts for generation of chimeric animals, and finally (3) Ceratin of targeted mutations in genes implicated in human genetic disorders. Extension of ES cell technology into a species larger than the mouse will add a new dimension to current effort to generate animal models of human genetic diseases. Such animals will advance our understanding of basic mechanisms involved in genetic diseases, and provide model systems for advancing new pharmacologic or genetic approaches to their treatment. In particular, these animals will be more versatile than the mouse for many types of physiological investigations, and may reproduce more accurately the human phenotype resulting from certain gene defects.